1. Field of the Invention
The present invention relates to a system and a method for adjusting the white balance of a projector type color display device.
2. Description of the Prior art
In color projectors (viz., projector type display devices), "white balance adjustment" is usually carried out at the time when the projectors are still in a manufacturing line and/or they are brought to a user's setting place. As is known, by properly adjusting the white balance of the color projector, the color image on the screen can have a natural color tone. However, in the color projectors of a type wherein images on display surfaces of three (viz., Red, Green and Blue) color display TV tubes are projected onto a screen to form a colored image thereon, the white or color balance of the projector is easily out of tune due to complicated arrangement of the three display TV tubes. Thus, in the color projectors of such type, the white balance adjustment is always necessary when the setting place and setting orientation of the projector change. Furthermore, such white balance adjustment becomes necessary when the projectors are used for a long time.
Hitherto, the white balance adjustment at the manufacturing line has been made by using color sensors. That is, the color sensors are manually attached to the display faces of the three display tubes for sensing the colors displayed on the display faces. All white signals (such as 5IRE signal and 100IRE signal) are fed to each display tube as an external signal, and the white balance adjustment of the color projector is carried out with reference to the information signals issued from the color sensors. One of the methods of this type is described in Japanese Patent First Provisional Publication 3-236699.
The white balance adjustment at the user side has been made by using a colorimeter and a color-difference meter. That is, the adjustment has been made manually by an inspector who compares, with his or her eyes, the color image on the screen and the reference color data provided by the colorimeter and the color difference meter.
However, it is difficult or at least troublesome to adjust the white balance by using the above-mentioned conventional adjusting methods. In fact, attaching and detaching the color sensors to and from the display tubes on the manufacturing line are troublesome. This becomes much more severe when a plurality of stackable color display devices, which are used for forming a so-called "multiscreen", are subjected to the white balance adjustment. Furthermore, the white balance adjustment by using the colorimeter and the color-difference meter requires a great deal of skill.